This invention relates to livestock feed, and more particularly to a method of preparing a livestock feed and feeding of livestock to increase utilization of protein by ruminant animals.
Numerous methods are described in the prior art for treating feed for ruminant animals so that fed protein does not undergo degradation by microorganisms located in the rumen of the animal. Prior art methods include chemical treatments of feed as disclosed in U.S. Pat. No. 3,507,662 and U.S. Pat. No. 3,619,200. However, these methods are not widely accepted as they have been found to render a large portion of fed protein unavailable for digestion in the post-rumen tract. Also, the chemicals themselves are often undesirable for various reasons. For instance, U.S. Pat. No. 3,619,200 protects fed protein by chemical modification with formaldehyde but formaldehyde is not approved for use in feeds in the United States by the Food and Drug Administration due to toxicity concerns.
Heat treatments to protect fed protein from degradation by ruminal microorganisms are also described in the prior art. U.S. Pat. No. 3,695,891 is an early example of the use of heat treating. Heat treatment reduces degradability by reducing protein solubility and by blocking sites of enzyme attack through temperature-induced chemical reactions between components of the feed. However, heat treatments described in the early prior art did not recognize that heat treating to protect fed protein is a very sensitive reaction. It is now known that too little heat provides very little protection to the fed protein while too much heat renders the treated protein indigestible in the post-rumen track.
U.S. Pat. Nos. 4,957,748, 5,023,091 and 5,064,665 teach that the efficiency of utilizing protein in feed by ruminants may be increased by mixing a protein-containing feed and a reducing carbohydrate and subsequently heating at a temperature, pH and time to reduce degradability of the feed protein by rumen microorganisms. The resistance to degradability is due in large part to protected protein forms formed during a set of chemical reactions known as the early Maillard reactions. Early Maillard reactions are thoroughly discussed in U.S. Pat. Nos. 4,957,748, 5,023,091 and 5,064,655 and those discussions are specifically incorporated herein by reference. Briefly, the early Maillard reactions comprise a reversible condensation between the carbonyl group of a reducing sugar and the amino groups of a protein to form substituted sugar amines. The conversion of the free amino groups of fed proteins to a substituted form results in protein molecules resistant to microbial proteases present in the rumen. Once past the rumen, the condensation product between the reducing carbohydrate and the amino groups of the protein is free to undergo hydrolysis and the fed protein is therefore available for digestion in the post-rumen tract. The heating step necessary to induce early Maillard reactions is commonly termed xe2x80x9cbrowningxe2x80x9d.
Addition of reducing carbohydrates to protein-containing feeds and subsequent browning has proven to be an effective means of increasing the proportion of undegraded intake protein (UIP) in ruminant animal feeds. Current commercial application of the technology commonly utilizes lignin sulfonate, a xylose-containing byproduct of the wood pulping industry, as a source of reducing carbohydrate to promote the early Maillard reaction. However, these reactions may be carried out with a large variety of commercially available reducing carbohydrates.
Although food science technology has advanced admirably in identifying methods to reduce ruminal protein degradability, the current technology is still deficient for several reasons. First, because present technology generally relies on the addition of reducing carbohydrates to protein-containing feed, this can impact on the dilution of protein, thus making the finished product less nutritionally efficient. Second, the addition of reducing carbohydrates to protein-containing feeds also makes the feed less conducive to shipment over long distances due to added bulk. Third, some existing treatment methods appear to significantly reduce the bioavailability of proteins in the post-rumen track resulting in a feed with lowered nutritional efficiency. Inferior availability of the amino acid lysine is often due to undesirable protein modifications. Fourth, reducing carbohydrates must be purchased, shipped and typically stored prior to their use in feed browning processes. The operational costs associated with purchasing and maintaining such supplies and associated handling equipment are relatively high. Thus, an improved method of manufacturing a protein-containing feed with reduced ruminal protein degradability that would alleviate the above-mentioned problems is desirable.
In one embodiment of the invention, a ruminant animal feed is manufactured by first mixing together a protein and carbohydrate-containing material suitable for livestock feed and a carbohydrase enzyme where the carbohydrase enzyme is effective in hydrolyzing carbohydrate molecules contained within the material. The mixture is then steeped at a temperature, pH and percent moisture for a time sufficient for the carbohydrase enzyme to effectively hydrolyze a portion of the carbohydrates contained within the material to their reducing forms. Following steeping, the mixture is heated at a temperature and time sufficient to: (1) significantly lower the degradability of proteins contained within the material to microorganisms in the rumen; and (2) maintain relatively high protein bioavailability in the post-rumen tract.
This method has the advantage over prior art methods in that it requires no additions of reducing carbohydrates from external sources. The enzymatic treatment allows conversion of a sufficient amount of carbohydrate molecules within the feedstuff itself to reducing forms to allow adequate protein protection in the subsequent heating, or browning, step. Thus, the feedstuff material, while having a protein content with reduced ruminal degradability, also has not been diluted by the addition of large amounts of reducing carbohydrates as required in some prior art methods. The cost of purchasing reducing carbohydrates and handling them is also eliminated by this method. In addition, the problem of shipping unnecessarily bulky feedstuffs is reduced.
As an alternative approach in the manufacturing method, the enzyme may be added to the steeping reaction in the form of a microorganism that secretes the particular carbohydrase enzyme or enzyme mixture. Suitable microorganisms may include fungi or bacteria. The microorganism may be in the form of a by-product from another industrial process such as brewer""s yeast discarded from the brewing process.
In another aspect of the invention, there is provided a method of feeding animals a feedstuff with reduced ruminal protein degradability. This method includes the steps of selecting a protein-containing feed suitable for a ruminant animal, and feeding to the ruminant animal a product formed by mixing the protein and carbohydrate-containing feed and a carbohydrase enzyme so that, after steeping and browning, the product has a protein content substantially resistant to degradation by rumen microorganisms.
In yet another embodiment of the invention, a method of hydrolyzing carbohydrates in carbohydrate-containing material is provided. A carbohydrate-containing material suitable for livestock feed is mixed together with a carbohydrase enzyme so that the carbohydrase enzyme may hydrolyze the carbohydrates to reducing forms. The resulting material is useful in the subsequent preparation of ruminant animal feed.
Accordingly, it is an object of the invention to produce a novel method for preparing a feed which reduces the ruminal degradation of protein-containing feed in a manner superior to prior methods.
It is a further object of the invention to provide a novel method for preparing a feed which provides improved digestibility of undegraded intake protein in the post-rumen tract.
It is another object of the invention to provide a method of making a protein-containing feed resistant to ruminal microorganism degradation where the method of manufacture requires no substantial dilution of protein content.
It is a further object of the invention to provide a novel method for feeding livestock a feed with decreased ruminal protein degradability.
Various other features, objects and advantages of the invention will be made apparent from the following description.
The method of making a ruminant animal feed according to this invention is initiated by selecting a protein and carbohydrate-containing material that is known to be suitable as an animal feed. The source of the protein and carbohydrate-containing material is not significant as long as it is a material suitable for livestock and such materials are well-known. Protein/carbohydrate sources may include oil seeds, grains, bean meal, sunflower seed meal, peas, canola meal, soybean meal, peanut meal, cottonseed meal, safflower meal, sesame meal, linseed meal, early bloom legumes, meat and bone meal, silages, corn gluten meal, by-product protein feedstuffs, milk products, poultry products, brewers grains, distillers grains, wheat middlings, soybean hulls, hays, corn, wheat, barley, sorghum, alfalfa, and mixtures thereof. The preferred protein and carbohydrate-containing material is soybean meal.
A carbohydrase enzyme is then selected and added to the protein and carbohydrate-containing material. As a general class, carbohydrase enzymes may be viewed as enzymes capable of breaking polysaccharides, oligosaccharides and disaccharides down into smaller carbohydrate units, many of the smaller units being reducing carbohydrate species. Representative carbohydrates include starches, dextrins, fibers, polysaccharides, sugars, pectins, amylose, amylopectin, cellulose, hemicellulose, xylans, pectic substances, arabinans, mannans, glucans, dextran, inulin, arabans, arabinoxylans, oligosaccharides, disaccharides, maltose, maltotriose, sucrose, lactose, raffinose, stachyose, gums and mixtures thereof.
A carbohydrase enzyme suitable for the invention may be from plant, animal, or other origin and include but is not limited to, invertase, xcex1-galactosidase, xcex1-amylase, amyloglucosidase, cellulases, hemicellulases, pentosanases, arabinofuranosidase, xylanase, amylases, glucoamylase, endoglucanase, pectic enzymes, pectin methylesterase, polygalacturonase, isomaltase, isoamylase, cyclomaltodextrinase, pullulanases, isopullulanase, hydrolases, glucosidases, dextranases, glucanases, galactosidases, mannanase, inulinase, and mixtures thereof. This list should not be considered inclusive of all carbohydrase enzymes suitable for use with this invention. Enzymes having vastly different catalytic mechanisms than those listed but with similar carbohydrate hydrolyzing abilities will also be suitable. The preferred carbohydrase enzyme is invertase.
Amounts of enzyme(s) needed for the hydrolysis of carbohydrates are dependent on the enzyme activity found in the specific enzyme source used. The number of units of a specific enzyme needed is a function of, among other factors, the amount and source of substrates, amount of reducing sugars desired, steeping time and temperature, water activity, pH, and combinations of enzymes used. For example, if steeping time is doubled, only around one-half the original number of enzyme units is needed to obtain similar results. The suggested range for invertase enzyme is about 8 Sumner units to about 800,000 Sumner units per 100 grams of soybean meal, dependent on aforementioned factors. One Sumner unit is the quantity of enzyme which will convert 1 mg of sucrose (in a 5.4% (w/v) sucrose solution at pH 4.5 and 20xc2x0 C.) to glucose and fructose in five minutes.
As an alternative approach, carbohydrase enzymes may be supplied to the manufacturing process by a microorganism where the microorganism produces the desired enzyme. The microorganism(s) may be fungi, protozoa, algae, bacteria, or combinations thereof. The microorganism may further be supplied in the form of a commercial by-product such as brewer""s yeast discarded from a brewery. Baker""s yeast (Saccharomyces cerevisiae) may be added to a suitable feed at a level of 200,000 colony forming units (cfu) to 100 billion cfu per 100 g of soybean meal, depending on, among other factors, the amount and source of substrates (carbohydrates), amount of reducing sugars desired, steeping time and temperature, water activity, and pH. Suitable organisms include, but is not limited to, direct-fed microbials, fungi, protozoa, algae, bacteria, Saccharomyces cerevisiae, yeast cultures, active dry yeast, Candida utilis, Kluyveromyces marxianus, Torula yeast, brewers yeast, Aspergillus niger, Aspergillus oryzae, Bacillusspecies, Bacteroidesspecies, Lactobacillusspecies, Bifidobacteriaspecies, Trichoderma viride, Leuconostoc mesenteroides, Pediococcusspecies, Propionibacteriaspecies, Saccharomycesspecies, Streptococcusspecies, or combinations thereof.
The incubation of the mixture at suitable temperature, pH, moisture content and time is carried out in a steeping step. The temperature for the steeping step may be from about 20xc2x0 C. up to about 75xc2x0 C. although the particular steep temperature will depend on the particular enzyme or enzyme mixture being used. The preferred steep temperature is from about 45xc2x0 C. to about 65xc2x0 C. for the enzyme invertase. The pH for steeping may be from 4 to about 10.5 with the preferred pH being from about 5 to about 7. The steep may be allowed to run from around 10 minutes up to about 12 hours with about 40 to 90 minutes being the preferred time. Optimal steeping time is dependent, among other factors, on the amount and source of substrates (carbohydrates), amount of reducing sugars desired, steeping temperature, water activity, pH, and enzyme concentration. The amount of moisture added to the mixture may be up to about 40% by weight with about 10% to about 20% being preferred when using the soybean meal and invertase combination.
Following steeping, the mixture is heated to a temperature ranging from about 80xc2x0 C. to about 180xc2x0 C. for about 30 minutes to 3 hours to effectively brown the material. The preferred temperature is about 90xc2x0 C. to about 120xc2x0 C. for 45 minutes to about 90 minutes. During browning, reducing carbohydrates formed by the action of the carbohydrase enzyme undergo condensation reactions with free amino groups of protein molecules to form protein species resistant to degradation by microorganisms located in the rumen. Thorough discussion of the browning reaction can be found in U.S. Pat. Nos. 4,957,748, 5,023,091 and 5,064,665, each of which is specifically incorporated herein by reference.
The efficacy of a feedstuff prepared by the foregoing method is illustrated by the following nonlimitive examples. These examples are directed at showing reduced protein degradability qualities as well as improved protein bioavailability aspects of a feedstuff made according to the present invention.